The 2018 Magnitude 7.1 Earthquake Near Point MacKenzie, Alaska

On November 30, 2018, at 17:29, a magnitude 7.1 earthquake struck 1 km southeast of Point MacKenzie, Alaska, at a depth of 46.7 km. This event represents the sole strong earthquake recorded in the region since January 1, 2000, according to available data. The quake originated in south-central Alaska near the northern end of Cook Inlet, an area characterized by active tectonic processes. The broader geological setting of this region stems from its position along the convergent boundary where the Pacific Plate subducts beneath the North American Plate. This subduction drives the formation of the Aleutian volcanic arc and generates frequent seismicity throughout southern Alaska. Point MacKenzie lies within the Cook Inlet basin, underlain by thick sedimentary sequences accumulated over millions of years amid ongoing tectonic compression. The basin's structure reflects interactions involving the Yakutat microplate, which collides with the continent and contributes to regional deformation and uplift in the Chugach and Talkeetna mountains. Seismic history in south-central Alaska includes several notable events tied to the same subduction dynamics. The 1964 Great Alaska Earthquake, with a magnitude of 9.2, remains the largest recorded in North American history and caused widespread subsidence and uplift across the Cook Inlet area. Subsequent moderate to large events have punctuated the record, underscoring the persistent hazard from the megathrust interface at depths typically ranging from 20 to 60 km, consistent with the 46.7 km depth of the 2018 event. The 2018 earthquake's characteristics align with intraslab or interface seismicity common in this tectonic regime. Its location near Point MacKenzie highlights the proximity of population centers such as Anchorage to active fault systems. Ground shaking from the event was widely felt across the region, though detailed impacts fall outside the scope of this geological overview. Ongoing monitoring by seismic networks continues to refine understanding of strain accumulation along the subduction zone. Updated models incorporate data from events like the 2018 quake to assess long-term recurrence intervals and potential for future large-magnitude releases.

References

United States Geological Survey Earthquake Catalog Alaska Earthquake Center Seismicity Reports